1. Field of the Invention
The present invention relates to a power supply voltage regulator circuit for supplying power supply voltage to a normal circuit and backup system circuit, and a microcomputer.
2. Description of Related Art
Recently, in order to reduce power consumption and improve battery lifetime, some mobile devices e.g. digital video cameras are being made so that no power is supplied to the microcomputers embedded therein when in a state (a standby state) in which CPU operation is not necessary. However, even when in the standby state, power must be provided to the microcomputer's clock function and to memory such as backup RAM. Therefore, power is separated between CPU side normal circuit power and backup system circuit power so that when in the standby state, the supply of power to the normal circuit is stopped and power is supplied to the backup circuit.
In Japanese Laid-Open Unexamined Patent Application Publication No. S62-6315, a memory backup apparatus for microcomputers was set forth. For example, the microcomputer memory backup apparatus has a microcomputer that can back up memory at low power consumption, a reset circuit for sending reset signals when voltage is below a certain reference voltage, a backup power circuit for switching the power supply of the microcomputer to microcomputer backup power (such as lithium batteries) when voltage is below a certain reference voltage, and a power detection circuit for detecting whether or not there is power. Furthermore, the microcomputer is configured such that after a reset signal is detected from the reset circuit, the operation mode or low power consumption mode (standby mode) is executed by a signal from the power detection circuit.